Thin film thermal processor



April 1965 H. H. BELCHER ETAL 3,180,398

THIN FILM THERMAL PROCESSOR Filed 001;. 5. 1961 ATTORNEYS United StatesPatent 3,189,398 THEN FILM THERh iAL PRQCEdSOR Harold H. Beleher,Orange, and Douglas A. Rogers, Greenfield, Mass, assignors to RodneyHunt Machine (Iompany, Grange, Mass.

Filed Oct. 5, 1951, Ser. No. 143,148 6 Claims. (Cl. 159-6) Thisinvention relates to thin film thermal processors and more particularlyto a novel spreader blade construction for such processors.

Thermal processors of the thin film type are well known and one suchtype is described in US. Patent No. 2,774,- 415. These processors arecommonly used for evaporation or distillation and may be used for avariety of other heat or mass transfer processes. In the processor, theliquid feed material is introduced at the top of an externally heatedhollov cylinder, flows down the side walls of the cylinder by gravity asa thin film and is acted upon by a concentric bladed rotor.

Rotors commonly used at the present time are of two types. One typeutilizes metal blades having a small fixed cl arance from the cylinderwall and a second type utilized employs radially movable plastic orcarbon blades held in contact with the wall by centrifugal force orspring tension or both. Both types of rotors have certain disadvantages.

The fixed clearance blade rotors, for effective operation, must utilizea small clearance requiring very exact machining and set-up of bothcylinder and rotor. The plastic or carbon blades scraping the cylinderwalls are subiect to wear, in some cases severe wear when crystallineproducts develop as the volatile component is removed. The bladematerial worn away appears as a contamination in the product discharge.

The present invention avoids the above-mentioned difficulties byproviding an improved metal blade tip for spreading liquid film evenlyover all parts of a heated surface to obtain hi h rates of heat transferand uniform reatment of all material. The construction of the presentinvention substantially reduces blade wear while at the same timeobtaining uniformity of action even under conditions of moderatedeparture from exact circular cross-section of the cylinder or exactconcentricity of the rotor.

It is therefore a primary object of the present invention to provide animproved thin film thermal processor.

Another object of the present invention is to provide an improvedspreader blade construction for thermal processors.

Another object of the present invention is to provide a thermalprocessor spreading blade system capable of handling materials of a wideviscosity range with a minimum danger of material burn on.

Still another object of the present invention is to provide an effectivemetallic blade tip structure which is free of cracks, crevices or closeclearances where bacterial action may occur and which is readilyremovable and cloanable to meet sanitary standards.

These and further objects and advantages of the invention will be moreapparent upon reference to the following specification, claims andappended drawings wherein:

FIGURE 1 is an elevational view with parts in crosssection showing thenovel thermal processor of the present invention;

3,380,393 Patented Apr. 2?, 1955 FIGURE 2 is a partial horizontalsection through the processor of FIGURE 1; and

FIGURE 3 is an elevational view taken along line 3-3 of FIGURE 2.

Both the fixed blade and radially movable type bladed rotors presentlyused have certain disadvantages. The fixed clearance blades, foreffective operation, must use a rather small clearance in the order of0.025 to 0.650 inch requiring very exact machining and set-up of bothcylinder and rotor. Furthermore, the clearance may be subject to muchvariation due to distortion of both cylinder and rotor under operatingtemperature. With very thin films, the rotor blades may not touch thefilm and very high rotor speed is necessary to accomplish spreadingthrough fanning action alone. Such high speeds require a high powerinput and also produce undesirable splash eflects increasing thelikelihood of liquid droplets being carried out with the vapor stream.

With very thick films, the fixed clearance blades dip into the filmlevelling the film but trapping ahead of the blade a mass of liquid as afillet. The liquid in this fillet drops under the influence of gravitymuch faster than does the material spread on the cylinder wall whereviscous drag on the wall slows the downward motion. The final productdischarged is therefore a mixture of overtreated and undertreatedmaterial. Product quality suffers and it is difiicult to obtain uniformhighly concentrated product.

In a given process, the eitects of thin and thick films may both bepresent, since removal of the volatile component changes both the volumeand the viscosity of the remaining liquid. Fixed blade clearances andspeeds must therefore be chosen on the basis or" the best compromisewith conditions, and the choice is often very ineffective for certainstages of the process.

The radially movable plastic or carbon blades scraping the cylinder wallare subject to wear, in some cases severe wear, when crystallineproducts develop as the volatile component is removed. Blade materialworn away appears as contamination in the product discharge. The blades,usually interrupted by gaps between rubbing surfaces, produce a nearlydry wall after passage of the rubbing surfaces, resulting in burn on ofover-concentrated product and loss of heat transfer eificiency. Suchblades do not satisfactorily treat materials of high viscosity becauseof failure to respread the material on the wall scraped dry by thecontact portions of the blades, with consequent increase in the burn onof material.

The novel blade construction of the present invention avoids the abovedifliculties by providing a radially movable blade which provides auniform spreading action.

Referring to the drawings, FIGURE 1 shows the ther mal processor of thepresent invention generally indicated at Ill. The processor comprises avertical cylinder 12 having a portion surrounded by a heating jacket 14which may be supplied with steam or other heating fluid.

Material to be processed enters through inlet pipe 16, flows down theinner wall of the vertical cylinder 12 under the influence of gravityand discharges through conical collector 18 and discharge pipe 29.Vapors pro duced from the processed material discharged from outletconduit 22. A hollow concentric rotor 24 has its top and bottom shafts26 and 28, respectively, carried in suitable bearings 30 and 32. Lowerbearing 32 is supported by a spider 34 secured to the lower end ofcylinder 12. Rotor 24 carries a plurality of blades 36 extendingouttangential viscous drag force. balance position'of the blade tips 40is reached, deter- 3 I wardly from the rotor toward the inner surface ofcylinder 12.

FIGURES 2 and 3 show sectional and elevational views respectively of theblade assembly details. Blades 36 are welded or otherwise suitablyfastened to rotor 24 and extend radially outward as shown, terminatingin angle section 38 approximately parallel to the cylinder wall at theblade location. The blades are fitted with a vertically extending seriesof relatively short and relatively light metallic blade'tips 40. Theface of each right-angle terminal section 38 is punched with a verticalseries of rectangular holes 42 receiving reduced sections cream 44 ofblade tips 49. The vertical dimension of holes 42 is considerably lessthan the height of blade tips 40 and the vertical spacing'between holecenters is the blade tip height plus a small fraction of an inch.

The extended ear 44 along one end of each blade tip passes through aslot 42 in blade termination 38. The vertical dimension of each ear isslightly less than the vertical dimension of the holes 42. The ears 44are bent with an offset 46 to interlock with the holes. With the rotor24 within the cylinder 12 and the blades 36 and blade tips 40 engaged asshown in FIGURE 2, the blade tips are maintained in correct verticalspacing but can swing in a horizontal plane about one vertical edge ofholes 42. The blade tips 40, however, cannot be dis-' engaged from theblades 36. When the rotor is removed from'the cylinder, then the bladetips 40 may be swung further out so that offset 46 clears holes 42 andthe tips unhooked from the blades for cleaning.

The outer surfaces or working face 48 of each blade tip '40 is formed asshown and this formation is necessary for best performance of theprocessor. With the rotor turning in the clockwise direction of thearrow in FIGURE2, the blade tips 40 are drawn forward by the rearwardedgeof holes 42 in blades 36. Centrifugal force causes the blade tips 40to swing out about this edge as a pivot until they contact the film ofliquid 50 on the wall of cylinder 12. The working face 48 trailing fromits pivot point is shaped to gradually approach the wall of purposes ofcleaning and the blade tip structure is free of cracks, crevices orclose clearances where bacterial action may occur particularly whenoperating upon food or medicinal products.

, The invention may be embodied in other specific forms be considered inall respects as illustrative and not restrictive, the scope of theinvention'being indicated by the appended claims rather than by theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

What is claimed and desired to be secured by United States LettersPatent is:

l. A spreader blade assembly for thin internalfilm thermal processorscomprising an elongated rotor having a longitudinal axis, a plurality ofcoplanar outwardly extending blades carried by said rotor, a portion ofsaid blades being substantially parallel to said longitudinal axis, aseries of longitudinally spaced and longitudinally aligned. apertures inthe substantially parallel portion of each of said blades, and aplurality of longitudinally spaced. blade tips having portions pivotallyreceived in said apertures.

2. An assembly according to claim 1 wherein said apertures arerectangular.

3. A spreader blade assembly for thin internal film thermal processors,comprising an elongated rotor having a longitudinal axis, a plurality ofoutwardly extending blades carried by said rotor, a portion of saidblades being substantially parallel to said longitudinal axis, a seriesof longitudinally spaced and aligned apertures in the substantiallyparallel portion of each of said blades, and

cylinder 12 but blends into an outward curved portion 52 close to thetrailing edge of the working face 48. The angle of the working face withrespect to the adjacent wall surface of cylinder 12 decreases graduallytozero at the closest approach between blade surface and wall and thenincreases to raisethe trailing-edge slightly from the wall as indicatedat 54.

' -In operation with the rotation in the direction of the arrow inFIGURE 2, centrifugal force causes the blade tips 40 to swing outwarduntil a part of the working face of each blade contacts the liquid filmon the cylinder wall. Viscous drag'between the working face and theliquid film causes the liquid to accumulate slightly as a thickened film56 ahead of the point of minimum blade tip-to cylinder wall clearance.The blade tip planes or skis on this thickened area establishing a.balance between the radially outward centrifugal force and the radiallyinward planing or lift force in combination with the In this way, .adefinite mining the thickness of the liquid film 50 spread on the wallof the cylinder 12. Since the contour of the blade tip working face 48is shaped at the trailing edge with a curved section 52 graduallyreducing the planing angle to zero, a balance position and'consequent'spreading of an even film is assured whether the liquid film is thick 7rotor and cylinder alignment, will have a negligible eifect 'on theevenness of the spread film.

It is apparent from the above that the present invention provides anovel spreader blade construction for said chamber by the action ofcentrifugal force when a plurality of longitudinally spaced blade tips,said blade tips havinga reduced portion pivotally received through saidapertures, said reduced blade tip portion including an offset lockingsaid blade tips to said blades.

4. In a thin internal film thermal processor including a wall forming anelongated chamber of circular section, a spreader bladeassemblycomprising an elongated rotor rotatably mounted in said chambersubstantially concentric with said wall, a plurality of outwardlyextending blades carried by said rotor, said blades including an outerportion substantially parallel to the inner surface of said chamberwall, a series of longitudinally spaced and longitudinally alignedapertures in said outer portion of each of said'blades and a pluralityof longitudinally spaced blade tips, each of said blade tips having areduced portion pivotally received through a corresponding aperture,said reduced blade tip portion including an offset locking said bladetips to said blades.

5. An assembly according to claim 4 wherein each saidblade tip 'hasapairof straight edges and said tip is curved towards its edge remote fromsaid aperture whereby the convex side of'said blade tip curvatureis-brought into engagement with a fluid film on the inner surface ofsaid rotor is rotated.

' 6. A spreader assembly for thin internal film thermal processorscomprising a vertical elongated rotor, a plurality of rigid radiallyextending blades carried by said rotor, said blades terminating in aflat angle portion substantially parallel with the inner surface of aprocessor, a series of longitudinally spaced and longitudinally alignedrectangular apertures in the flat angle portion of each of said blades,and a plurality of longitudinally spaced and longitudinally disposedsubstantially flat blade tips having vertical edges, said blade tipseachhaving a reduced portion along one vertical edge pivotally receivedthrough a corresponding aperture, said reduced blade tip portionsincluding an offset locking said blade tips to said blades,

5 6 said blade tips being outwardly curved toward their trail- 2,546,3813/51 Zahm 1S9-6 ing vertical edges whereby the convex side of said blade2,774,415 12/56 Belcher 159-6 tip curvature is brought into engagementwith a fluid film 2,974,725 3/61 Samesreuther 159-6 on the Walls of aprocessor by the action of centrifugal 3,058,516 10/62 Brunk 1596 forcewhen said rotor is rotated. 5 FOREIGN PATENTS Eeferemes Qiteal by theExaminer 1,061, 93 7/59 Germany. UNITED STATES PATENTS 13683 11/59Germany- L3O8819 7/19 Taylor 159 6 m NORMAN YUDKOFF, Primary Examiner.2,542,270 3/51 Zahm 159-6 GEORGE D. MITCHELL, CHARLES OCONNELL,2,546,380 3/51 Zahm 1596 Examiners.

4. IN A THIN INTERNAL FILM THERMAL PROCESSOR INCLUDING A WALL FORMING ANELONGATED CHAMBER OF CIRCULAR SECTION, A SPREADER BLADE ASSEMBLYCOMPRISING AN ELONGATED ROTOR ROTATABLY MOUNTED IN SAID CHAMBERSUBSTANTIALLY CONCENTRIC WITH SAID WALL, A PLURALITY OF OUTWARDLYEXTENDING BLADES CARRIED BY SAID ROTOR, SAID BLADES INCLUDING AN OUTERPORTION SUBSTANTIALLY PARALLEL TO THE INNER SURFACE OF SAID CHAMBERWALL, A SERIES OF LONGITUDINALLY SPACED AND LONGITUDINALLY ALINGEDAPERTURES IN SAID OUTER PORTION OF EACH OF SAID BLADES AND A PLURALITYOF LONGITUDINALLY SPACED BLADE TIPS, EACH OF SAID BLADES TIPS HAVING AREDUCED PORTION PIVOTALLY RECEIVED THROUGH A CORRESPONDING APERTURE,SAID REDUCED BLADE TIP PORTION INCLUDING AN OFFSET LOCKING SAID BLADETIPS TO SAID BLADES.